U.S. patent application number 11/879559 was filed with the patent office on 2008-01-24 for servo-press with energy management.
Invention is credited to Martin Schmeink.
Application Number | 20080016940 11/879559 |
Document ID | / |
Family ID | 38626540 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080016940 |
Kind Code |
A1 |
Schmeink; Martin |
January 24, 2008 |
Servo-press with energy management
Abstract
In a press installation including a number of presses with
servo-drives for operating the presses and auxiliary equipment such
as workpiece handling devices wherein an energy management system
is provided including a DC voltage intermediate circuit connected
to a power supply grid via an AC/DC converter and to the
servo-drives via servo-converters, a fly-wheel storage device is
connected to the intermediate circuit for supplying energy thereto
and recapturing energy therefrom under the control of a control
arrangement which controls the flow of power between the
intermediate circuit, the servo-drives, the fly-wheel storage
device and the power supply grid.
Inventors: |
Schmeink; Martin; (Salach,
DE) |
Correspondence
Address: |
RONALD S. LOMBARD;PATENTS AND TRADEMARKS
4430 TWIN OAKS DRIVE
MURRYSVILLE
PA
15668
US
|
Family ID: |
38626540 |
Appl. No.: |
11/879559 |
Filed: |
July 18, 2007 |
Current U.S.
Class: |
72/435 ; 322/4;
72/20.1; 72/347; 72/445 |
Current CPC
Class: |
B30B 15/148 20130101;
B21D 43/05 20130101 |
Class at
Publication: |
72/435 ; 322/4;
72/20.1; 72/347; 72/445 |
International
Class: |
B21D 24/02 20060101
B21D024/02; B21D 24/12 20060101 B21D024/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2006 |
DE |
10 2006 033 562.7 |
Claims
1. A press installation, particularly for forming large parts,
comprising: a number of presses (2, 3, 4) representing different
press stages, each including a stationary press table (14-16), a
plunger (5, 6, 7) movable relative to the press table (14-16) and a
servo-drive (8-13) for operating the press (2,3 4); a parts
transport arrangement (22), with workpiece engagement structures
(23, 24) for moving workpieces into and out of the presses (2, 3,
4) and a servo-drive (20, 21) for operating the transport
arrangement; a DC voltage intermediate circuit (34) connected to a
power supply grid (46) via an AC/DC converter (45) and to the
servo-drives via servo converters (28-33); a fly-wheel storage
device (48) connected to the DC intermediate circuit (34) via a
voltage converter (52) for supplying energy to the DC intermediate
circuit (34) and for recapturing excess energy therefrom; and, a
control arrangement (35) connected to the converters (45, 28-33,
52) for controlling the flow of power between the DC intermediate
circuit (34) and the servo-drives (8-13, 20, 21), the fly-wheel
storage device (48) and the power supply grid (46).
2. The press installation according to claim 1, wherein the control
arrangement (35) is additionally connected to the DC voltage
intermediate circuit (34) for monitoring the voltage therein.
3. The press installation according to claim 1, wherein the control
arrangement (35) controls the servo-drives (8, 20) in accordance
with the working procedures for the workpieces.
4. The press installation according to claim 1, wherein the control
arrangement (35) controls the AC/DC converter (45) and the
fly-wheel storage device (48) during operation of the press
installation (1) in such a way that the power supply from the power
grid (46) is maintained within predetermined limits.
5. The press installation according to claim 1, wherein the control
arrangement (35) maintains the limits of the power conversion in
the AC/DC converter (45) for the supply of power from the grid (46)
and also for the feedback of power into the power supply grid
(46).
6. The press installation according to claim 5, wherein the power
limits are so selected that the utilization of the fly-wheel
storage device (48) is maximized.
7. The press installation according to claim 5, wherein the power
limits are so selected that the speed curve for the fly-wheel
storage device (48) is the same in all subsequent press cycles.
8. The press installation according to claim 5, wherein power
limits are so selected that the grid (46) load is minimized.
9. The press installation according to claim 1, wherein the control
arrangement (35) controls the AC/DC converter (45) and the
fly-wheel storage device (48) during the operation of the press
installation (1) in such a way that the power supply from the power
supply grid (46) remains constant.
10. The press installation according to claim 1, wherein each of
the servo-converters (28-33, 52) is provided with a power sensing
device (42, 43, 44, 51) which is connected to the control
arrangement (35) for supplying to it a signal indicative of the
amount of power actually converted by the servo-converters.
11. The press installation according to claim 10, wherein the
control arrangement (35) integrates the power amounts processed by
the servo-drives (28-33, 52) during a press cycle in order to
determine the energy used by each servo-drive (28-33, 52) during
each press cycle.
12. The press installation according to claim 11, wherein the
control arrangement (35) determines the sum of the energy used by
the servo-drives (28-33, 52) and controls the AC/DC power converter
(45) such that it retrieves from the power supply grid (46) a
corresponding amount of energy.
13. The press installation according to claim 1, wherein the
control arrangement (35) controls the fly-wheel storage device (48)
in such a way that during a stationary operation of the press
installation (1) the energy stored therein at the beginning of a
press cycle is the same as at the end of a press cycle.
14. The press installation according to claim 1, wherein the
control arrangement (35) controls the fly-wheel storage device (48)
in such a way, that, at any time during a press cycle sufficient
storage capacity is available for accommodating energy feed back to
the fly-wheel storage device during an emergency shut-down of the
press installation (1).
15. The press installation according to claim 14, wherein the
control arrangement (35) controls the fly-wheel storage device (48)
in such a way that, during an emergency shut-down of the press
installation (1), the control arrangement (35) can take up grid
(46) energy in order to reduce the grid (46) load in a controlled
manner from the operating value to zero.
16. A method of operating a press installation, particularly a
large part press installation, comprising: a number of presses (2,
3, 4) representing different press stages, each including a
stationary press table (14-16), a plunger (5, 6, 7) movable
relative to the press table (14-16) and a servo-drive (8-13) for
operating the press (2,3 4); a parts transport arrangement (22)
with workpiece engagement structures (23, 24) for moving workpieces
into and out of the presses (2, 3, 4) and a servo-drive (20, 21)
for operating the transport arrangement; a DC voltage intermediate
circuit (34) connected to a power supply grid (46) via an AC/DC
converter (45) and to the servo-drives via servo converters
(28-33); a fly-wheel storage device (48) connected to the DC
intermediate circuit (34) via a storage converter (52) for
supplying energy to the DC intermediate circuit (34) and for
recapturing excess energy there from; and, a control arrangement
(35) connected to the converter (45, 28-33, 52), said method
comprising the steps of maintaining and controlling the flow of
power between the DC intermediate circuit (34) and the servo-drives
(8-13, 20, 21), the fly-wheel storage device (48) and the power
supply grid (46) so as to limit variations in the power demands
from the power supply grid.
17. The method according to claim 16, wherein the control
arrangement (35) is connected to the DC voltage intermediate
circuit (34) for monitoring the voltage therein.
18. The method according to claim 16, wherein the control
arrangement (35) controls the servo-drives (8, 20) in accordance
with the working procedures for the workpieces.
19. The method according to claim 16, wherein the control
arrangement (35) controls the AC/DC converter (45) and the
fly-wheel storage device (48) during operation of the press
installation (1) in such a way that the power supply from the power
grid (46) is maintained within predetermined limits.
20. The method according to claim 16, wherein the control
arrangement (35) controls the AC/DC converter (45) and the
fly-wheel storage device (48) during operation of the press
installation (1) in such a way that the power supply from the power
grid (46) remains constant.
21. The method according to claim 16, wherein each of the
servo-converters (28-33, 52) is provided with a power sensing
device (42, 43, 44, 51) which is connected to the control
arrangement (35) so as to supply a signal to the control
arrangement (35) indicative of the amount of power actually
converted by the servo-converters.
22. The method according to claim 21, wherein the control
arrangement (35) integrates the power amounts processed by the
servo-drives (28-33, 52) during a press cycle in order to determine
the energy used by each servo-drive (28-33, 52) during each press
cycle.
23. The method according to claim 22, wherein the press
installation according to claim 11, wherein the control arrangement
(35) determines the sum of the energy used by the servo-drives
(28-33, 52) and controls the AC/DC power converter (45) such that
it retrieves from the power supply grid (46) a corresponding amount
of energy.
24. The method according to claim 16, wherein the control
arrangement (35) controls the fly-wheel storage device (48) in such
a way that during a stationary operation of the press installation
(1) the energy stored therein at the beginning of a press cycle is
the same as at the end of a press cycle.
25. The method according to claim 16, wherein the control
arrangement (35) controls the fly-wheel storage device (48) in such
a way, that, at any time during a press cycle sufficient storage
capacity is available for accommodating energy feed back to the
fly-wheel storage device during an emergency shut-down of the press
installation (1).
26. The method according to claim 25, wherein the controls
arrangement (35) controls the fly-wheel storage device (48) in such
a way that, during an emergency shut-down of the press installation
(1) the control arrangement (35) can take up grid (46) energy in
order to reduce the grid (46) load in a controlled manner from the
operating value to zero.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefits of German
Application No. 10 2006 033 562.7 filed Jul. 20, 2006.
BACKGROUND OF THE INVENTION
[0002] This invention resides in a press installation and in a
method of operating such an installation. The invention relates
particularly to large part-press installations, for example, in the
form of press-lines are on multistage large part presses in the
form of transfer presses.
[0003] Conventional presses include a mechanical press drive with
an electric drive motor and a fly-wheel which serves as an energy
storage device. A crank drive, a circular drive, an elbow drive or
a similar drive converts the rotation of the fly-wheel into a back
and forth movement of a plunger. The fly-wheel is so large
dimensioned that its speed changes remains tolerable. As a result,
it stores substantially more energy than is necessary for a single
deformation procedure. At least, if the fly-wheel is firmly
connected to the circular drive a correspondingly large amount of
energy needs to be destroyed when the press is stopped.
[0004] Lately, more and more considerations are given to
servo-presses which include servo-motors for driving the plunger
and also auxiliary equipment. These servo-motors drive the plunger
on the respective other equipment of the press without the use of a
fly-wheel. Consequently, the respective servo-motor must provide
the power peaks required by the plunger or other equipment.
[0005] German publication DE 10 2005 026 818 A1, for example,
discloses a press with a drawing die which is provided with
electric drives. The electric drives are connected to the drives
for the main movement of the plunger and/or the auxiliary movements
of workpiece transport elements by way of an, at least sequentially
usable guide shaft and, on the other hand, by way of energy storage
devices and/or energy exchange modules.
[0006] The connection between the main drives and the auxiliary
drives and the drawing dies by way of guide shafts and energy
exchange modules however is quite expensive.
[0007] Furthermore, German publication, DE 198 21 159 A discloses a
deep-draw press whose plunger is driven by servo-motors via
spindles. The drawing die is also driven by servo-motors via
spindles. The servo-motors of the drawing die are also
interconnected by electrical shafts. Both servo-motors are
controllable by a program computer.
[0008] Servo-motor controlled machines cause varying loads on the
power supply grid. This may cause excessive loads on the power
supply grids. This may cause a problem occasionally already with a
single machine, but is very problematic if several machines working
in parallel are at peak loads all at the same time. In spite of
efficient drive techniques, this may lead to energy losses which
need to be avoided.
[0009] It is the object of the present invention to provide an
improved servo-press installation which avoids excessive power
supply peak requirements.
SUMMARY OF THE INVENTION
[0010] In a press installation including a number of presses with
servo-drives for operating the presses and auxiliary equipment,
such as workpiece handling devices wherein an energy management
system is provided including a DC voltage intermediate circuit
connected to a power supply grid via an AC/DC converter and to the
servo-drives via servo-converters. A fly-wheel storage device is
connected to the intermediate circuit for supplying energy thereto
and recapturing energy therefrom under the control of a control
arrangement which controls the flow of power between the
intermediate circuit, the servo-drives, the fly-wheel storage
device and the power supply grid.
[0011] The press installation according to the invention provides
an intermediate DC power supply circuit connected to the power
supply grid, or network, by way of a controlled power converter.
This intermediate DC power supply circuit supplies power to all
servo-drives for the plungers and all the servo-drives of the
auxiliary equipment such as part transport arrangements or
intermediate storage devices, drawing dies, etc. The respective
servo-drives are all supplied with power from the same intermediate
DC power supply circuit preferably via DC/AC converter devices. The
intermediate DC power supply circuit also includes a fly-wheel
storage device which is capable of taking energy from the
intermediate DC power supply circuit and also to return energy to
the intermediate DC power supply circuit. A supervisory control
arrangement controls the operation of the power converter devices.
In this way, the variations of the power withdrawn from the
electrical power supply grid can be minimized and the overall-power
requirements for the whole press installation remain essentially
constant. This substantially reduces the resistance losses in the
power supply lines which increase with the square of the current
flow. In addition to a reduction in losses, the power supply grid
quality is increased since load-induced voltage variations in the
power supply are minimized. Furthermore, expenses for the power
supply connections are substantially reduced since they do not need
to be de-energized for the peak power requirements of the presses,
but only for the average power requirements. With the intermediate
DC voltage power supply circuit and the DC/AC converters disposed
between the press drives and fly-wheel, the servo-motors of the
press drives and the fly-wheel can be operated independently at
different speeds. The converters practically form an electrical
infinitely variable transmission.
[0012] The control arrangement controls the power converter
arrangement, also called power supply unit, and determines whether
it supplies power to this intermediate DC power supply circuit,
also called the DC bus or returns energy therefrom. Predetermined
current flow limits are observed in the process. The current limits
may be determined dynamically. The control arrangement may
furthermore supervise the speed of the fly-wheel storage device and
the intermediate circuit voltage. It may control the supply and
return of energy from the power supply grid to the DC lines and
back based on the following values:
[0013] upper limit of the power storage fly-wheel speed;
[0014] lower limit of the power storage fly-wheel speed;
[0015] desired value of the fly-wheel speed;
[0016] actual fly-wheel speed;
[0017] desired value of the intermediate circuit voltage;
[0018] actual value of the intermediate circuit voltage.
[0019] The control is performed preferably with the aim of
minimizing power supply load peaks, that is, to establish a uniform
power supply load. For activating the fly-wheel storage device, the
dropping and raising of the intermediate circuit voltage can be
measured as this is the result of differences between the energy
consumption and energy supply from the grid. If limits are provided
for the withdrawal of energy from the grid and for the return of
energy into the grid with load peaks or return peaks differential
amounts remain, which must be taken from the fly-wheel storage
device or returned to it.
[0020] If the immediate circuit voltage drops, the slow-down
process for the fly-wheel storage is initiated, that is energy is
taken from the fly-wheel storage until the intermediate circuit
voltage has reached the original value. If the intermediate circuit
voltage rises, energy is supplied from the intermediate circuit to
the fly-wheel storage which is accelerated thereby. The fly-wheel
is accelerated until the intermediate circuit voltage has dropped
to the original, that is, the desired value.
[0021] With the dynamic variability of the current limits for the
supply of energy from, and the return of energy to, the grid, the
supply-and-return energy flow can be controlled. The current limits
for the supply and return of energy are separate parameters and are
controllable dynamically from without. By changing the current
limit of the supply unit the point at which the energy supply is
supplemented by the fly-wheel storage can be varied. By changing
the return current limit of the power supply unit, the point at
which energy is absorbed by the fly-wheel storage can be
varied.
[0022] With regard to the fly-wheel speed, the following operation
is possible: After switching on the servo-press, first the
fly-wheel of the fly-wheel storage device is accelerated to the
desired speed which is about 2/3 of maximum speed. At 2/3 of
maximum speed the fly-wheel storage device is ready for supplying
energy with a reduction of the speed and also for taking up energy
by acceleration of the fly-wheel from 2/3 of maximum speed to
maximum speed. In order to achieve a uniform grid power supply load
or possible, the current limits are reduced to such an extent that
the power peaks are provided for as much as possible by the
fly-wheel storage unit. In this way, the speed change reaches
maximum. The fly-wheel speed changes between maximum speed and a
minimum speed of almost zero.
[0023] The energy profile, that is, energy need depending on time
of a servo-press depends on:
[0024] the deformation work;
[0025] the movement profile;
[0026] the number of cycles per minute.
[0027] Therefore, an optimum determination of the current limits
for the manufacture of a part is possibly not optimal for the
manufacture of another part. As a solution, the current limits of
the power supply unit can be determined iteratively starting and
from a base setting. The current limits are initially reduced to
such an extent and for such a period until the fly-wheel storage
device reaches during operation the upper and the lower limit
speeds. In this regard, it can also be supervised whether the
fly-wheel reaches the desired speed within a press cycle.
[0028] The data determined for a particular part, that is,
workpiece, particularly the current limits for the energization of
the DC busses from the grid and for the return of energy from the
DC bus to the grid can be recorded specifically for each workpiece
data stage device. Later this data is available, so that it does
not have to be re-determined.
[0029] Instead of current limits, that is,--limit value for the
current, also power limits, that is--limit values for the power
that can be used, wherein the above description applies
correspondingly. There is an advantage in using power limits
because of the independence of the validity of the stored limit
values for the initially possibly non-constant grid voltage.
[0030] With the limitation of the current as power supply to the
converter arrangement and the current or power limitation for the
return to the grid, for the converter arrangement building
components designed for certain normal currents and peak currents
can be used which are substantially lower than the peak currents
needed by the press installation. As a result, the converter
arrangement may be smaller and the costs therefore are reduced.
[0031] The fly-wheel storage device is, with respect to the storage
capacity, so dimensioned that a predetermined partial amount of its
maximum capacity is sufficient to buffer all load changes occurring
in the press installation. The difference between this partial
amount and the maximum capacity of the fly-wheel storage device
corresponds to the maximum brake energy to be taken up by the
fly-wheel storage device driving an emergency shut down of the
press installation. In this way, it is made sure, on one hand, that
the fly-wheel storage device can be used for providing for a
totally uniform power supply grid loading whereas, on the other
hand, all drives of the press installation can be shut down in a
controlled, synchronous manner. After an emergency shut-down of the
press, the fly-wheel storage device runs at maximum speed. There is
no need to return power to the power supply grid.
[0032] Alternatively, the fly-wheel storage device may be
dimensioned somewhat smaller, so that during an emergency stop it
can accept at least a large part of the brake energy released by
the press installation during an emergency shut down while the
system is changed from grid loading to supplying power to the grid
in a controlled manner.
[0033] The control arrangement may be such that the power used at
the servo-drive arrangements is recorded. This can be done, for
example, by measuring the voltages and currents over time as
provided to the servo-motors. Additionally or alternatively, power
measuring devices may be provided at the converter arrangements.
If, for example, the DC currents entering the converter
arrangements and the respective voltages are measured, the
effective power can be determined herefrom in a simple and safe
manner.
[0034] On one hand the control arrangement can integrate the
momentary power applied during a press cycle at each converter
arrangement or, respectively, each servo-motor, and, therefore
determine the energy consumed or fed back by the respective drive.
The sum of the energy amounts measured or calculated for the
individual drives represents the amount of energy that needs to be
withdrawn from the grid during a press cycle. If this energy amount
is divided by the duration of a press cycle, the energy input to
the intermediate DC voltage circuit for which the converter
arrangement should be adjusted is obtained which also represents
the grid load. Under the press cycle, in this regard, a complete
upward and downward stroke of the plunger, that is, one operating
cycle of the press is to be understood. The beginning and the end
of such a press cycle does not need to be counted from a plunger
dead-end, but they can be selected in any way. For a multi-stage
press beginning and end points for a working cycle are all the same
for all the elements, that is for all elements and all the
servo-drive arrangements of the press installation.
[0035] While the control arrangement consequently controls on one
hand the converter arrangement depending on the energy requirements
needed for one press cycle, it can control on the other hand, the
fly-wheel energy storage depending on the momentary power output of
the individual servo-drive devices. If the converter arrangement is
controlled based on the energy balance, the fly-wheel energy
storage device is controlled based on the power balance. The
fly-wheel energy storage device compensates at any time for the
difference between the actual power consumption of the press and
the power withdrawn from the grid.
[0036] The control arrangement may additionally monitor the voltage
of the intermediate DC voltage circuit. This voltage does not
necessarily have to be kept constant. It is, however, expedient to
maintain that voltage within reasonable limits so as to avoid
excessive voltages on one hand and, on the other, to prevent a
voltage drop to values insufficient for the operation of the
converter.
[0037] When determining the control strategy for all the
converters, preferably, first all servo-drives receive control
signals without consideration of possible load peaks. Possibly
occurring load peaks are accommodated by the fly-wheel storage
device. Consequently, the operator is free to set the number of
press strokes, the deforming forces, the accelerations, etc. in an
expedient manner. He can utilize the capacity of all the drives to
the maximum without taking into consideration the power needs for
the whole press installation.
[0038] The invention will become more readily apparent from the
following description thereof on the basis of the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 shows a press installation with servo-drives for the
plungers and auxiliary equipment in a schematic representation;
[0040] FIG. 2 shows a press installation in the form of transfer
presses with several servo-motor operated press stages and
servo-motor operated auxiliary equipment;
[0041] FIG. 3 shows electric power supply arrangement for the
presses of FIG. 1 or 2;
[0042] FIG. 4 shows various diagrams representing the power
requirement of the various servo-drives and the fly-wheel storage
device; and,
[0043] FIG. 5 shows a diagram for the dimensioning of the capacity
of the fly-wheel storage device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] FIG. 1 shows a press installation 1 including at least one,
but in the shown example several, individual presses 2, 3, 4. The
presses are provided for a stepwise deforming of a workpiece, for
example, a metal sheet such as a vehicle body part, or similar,
which is treated in one press after another. The press 2 is a
drawing press, whereas, the presses 3 and 4 are follow-up presses.
Each press 2, 3, 4 has a plunger 5, 6, 7. For driving the plunger 5
at least one, but preferably several servo-motors 8, 9 are
provided. Likewise, the plungers 6, 7 are driven by servo-motors
10, 11, 12, 13. The servo-motors 8 to 13 drive the plunger 5, 6, 7
by means of a suitable drive such as a spindle drive. Also other
drives may be used such as linear motors or similar drives. Below
the plunger 5 to 7 there is in each case a press table 14, 15, 16.
For deforming the workpiece, tools 17, 18, 19 are used, each
including a ball arm part 17a, 18a, 19a disposed on a press table
14, 15, 16. The respective upper tool part 17b, 18b, 19b is mounted
to the respective plunger 5, 6, 7. The tool 17 is a drawing tool.
The ball arm part 17a works together with a drawing die which uses
one or more servo-drives 20, 21.
[0045] In order to provide for a workpiece transfer, workpiece
transfer arrangement 22 is provided and which may include one or
more feeders 23 and handling units 24. The handling units 24 are
provided with several grippers for moving metal sheets onto the
tools 17, 18, 19, and again out of these tools. Between the presses
2, 3 and 3, 4 intermediate storage devices 25, 26 may be provided
in order to move the metal sheets into the tools 17, 18, 19 and
remove them from the tools. Also these interim storage devices are
devices which may include servo-drives.
[0046] FIG. 2 shows a press installation 1' in the form of a
transfer press. This press installation 1' is different in as much
as it does not exhibit the separate press frames of the presses 2,
3, 4, but the presses are combined to have a common transfer press
rack, that is they have a common frame. The arrangement includes
one or several plungers 5, 6, 7. The description above also applies
to the embodiment of the press installation 1' according to FIG. 2,
wherein however, the interim storage structures 25, 26 may be
omitted.
[0047] FIG. 3 shows schematically the electrical drive system 27 of
the press installation 1 for energy management. The drive system
includes all the electric servo-motors covered by the energy
management concept. In FIG. 3 are, as an example, the servo-motors
8, 9, 10, 11 of the presses 2 and 3 for driving the plungers 5, 6
and the servo-drives 20, 21 of the drawing dies shown. Energy is
supplied to these servo-motors 8 to 11 and 20, 21 via converter
units 28, 29, 30, 31, 32, 33 from a common DC voltage intermediate
circuit 34. The converter units 28 to 33 convert the DC voltage to
an alternating voltage of desired frequency and current for driving
the servo-motors 8, 9, 10, 11, 20, 21. A control unit 35 is
provided which controls the individual converter units 28 to 33. It
includes corresponding control outputs 36, 37, 38. It also has
control inputs 39, 40, 41 provided with equipment 42, 43, 44 for
determining or sensing the power consumption in the servo-motors 8,
9, 10, 11, 20, 21. The equipment 42, 43, 44 may, for example, be
means capable of sensing the current supplied by the DC voltage
intermediate circuit 34 to the converters 28 to 33. Power is
supplied at a given voltage to the DC voltage intermediate circuit
in the most simple case may be by an uncontrolled converter,
preferably, however, by a controlled converter, from a supply grid
46. A power monitoring device 47 may be used to generate a signal
representative of the power delivered from the converter 45 to the
DC voltage intermediate circuit 34, which signal is supplied to the
control unit 35.
[0048] The drive system 27 further comprises a fly-wheel storage
unit 48, including a motor 49 and a fly-wheel 50. The power
supplied to the fly-wheel storage unit 48 and the power supplied
thereby can be monitored by a power monitoring device 51 in the
connecting line between the DC voltage intermediate circuit 34 and
a converter 52 and the information can be supplied via a control
line to the control unit 35.
[0049] While in FIG. 3 several selected servo-motors together with
the respective converters are shown, it is to be understood that
the drive system 27 may include all the servo-motors, to which
power is supplied from the DC voltage intermediate circuit.
[0050] The press installation 1 and 1' and the drive system 27
operate as follows:
[0051] For the operation of the press installation 1, first the
curves or schedules of movement of the individual servo-motors 8,
9, 10, 11, 20, 21 based on a central press operating schedule are
determined, for example, by recording them in the form of a data
set or manual programming. The press installation is then placed
into operation by activating the converter 45 and supplying DC
voltage to the DC voltage intermediate circuit 34. Via the
converter 52, the fly-wheel storage device 48 is charged with a
buffer energy that is an amount of energy which is required to
buffer the load peaks occurring in the servo-motors 8, 9, 10, 11,
20, 21. The buffer energy P is shown in FIG. 5 as part of a maximum
storage energy M which can be stored by the fly-wheel storage
device 48. It is not greater than a maximum buffer value P.sub.max.
This value is so selected that a press installation 1 can be braked
down in an emergency and the remaining difference between maximum
energy M and maximum buffer energy P.sub.max is sufficient to
accommodate the energy released during braking.
[0052] Then the individual converters 28, 29, 30, 31, 32, 33 are so
controlled that the servo-motors 8, 9, 10, 11, 20, 21 perform the
desired movements. FIG. 4 shows the power supplied to, or released
by, the servo-motors 8, 9 plotted over the press angle .alpha.
which corresponds to a central press operating schedule step of 360
degrees of the press angle .alpha. which corresponds to the
revolution of an eccentric shaft of a conventional press and,
consequently, in connection with the press installation of FIGS. 1
an 2, a full power stroke and return stroke of the respective
plunger 5, 6, 7.
[0053] As apparent, the power uptake or release of the plunger
drive has in accordance with curve I a clear maximum which occurs,
for example, during the metal sheet deformation. Furthermore, there
may be a negative part which indicates energy back-feeding. The
servo-drives of the individual presses 2, 3, 4 may have different
power uptake curves and operate with phase displacement relative to
one another.
[0054] Another diagram shows a curve II which represents the power
uptake and release of the servo-motor 21 of the drawing die. A
clear back-feeding section is, for example, present specifically in
the area where the servo-motor of the plunger requires a
substantial power input.
[0055] Another curve III characterizes in an exemplary manner, the
power uptake of other equipment such as the intermediate storage
devices 25, 26 or the part transport arrangement 22.
[0056] The control arrangement 35 may be, for example, so designed
that it integrates the power uptake according to curves 1, II and
III and consequently determines the average power uptake required.
This integral amount is shown in FIG. 4 for each curve I, II, III
separately, that is, curves Ia Ia, IIIa. The overall integral, that
is the sum of the curves Ia, Ia, IIIa represents the electrical
energy uptake of the press installation 1 for a press cycle which,
based on the press angle .alpha. can be considered a constant power
supply VI, which is supplied by the power grid. In order to provide
for such a constant power supply requirement, the fly-wheel storage
device 48, buffers in each press cycle the power uptake and back
feeding in accordance with curve VII. In other words, the converter
52 is so controlled that, at any point in time, the power supplied
by the DC voltage intermediate circuit 34 corresponds to the
overall energy uptake, driving a press cycle divided by the
time-duration of a press cycle.
[0057] As apparent, the fly-wheel storage device 48 is exposed to
phases of energy uptake and phases of energy back feeding. Its
state of change is monitored by the control unit 35. It ensures
that the fly-wheel of the storage device 48 operates at the
beginning and the end of each press cycle with the same speed so
that, over time, it is neither charged nor discharged. Furthermore,
it ensures that the storage content does not exceed a value
P.sub.max at any time so that a power uptake capacity R, see FIG.
5, is always available in order to store all of the braking energy
released during an emergency shut down of the whole press
installation 1. In addition, the energy management by the control
unit 35 is preferably so operated that the energy content of the
fly-wheel storage device 48 drops during a press cycle never below
a minimum value P.sub.min. The minimum value P.sub.min is so
determined that the energy stored in the fly-wheel storage 48 is
always sufficient to finish a started press cycle if, at any time
during the press cycle, the grid power supply should fail, so that
all drives can be moved in an orderly manner and synchronously to a
safe position and collisions can be avoided. The minimizing energy
stored in the fly-wheel storage device 48 is preferably at least
large enough for performing a complete press cycle. Actually, it is
preferably somewhat higher, so that also after completion of a
press cycle, information technical equipment such as a computer
etc. can still be energized with a sufficient amount of energy.
[0058] A press installation with an energy management system
comprises a fly-wheel energy storage device which, on one hand, has
sufficient capacity for taking up the energy released during an
emergency shut down and, on the other hand, stores at any time
sufficient energy to permit an orderly completion of a press-cycle
should the grid power supply fail. A central control unit monitors
the operation of all servo-drive arrangements connected to a DC
voltage intermediate circuit and also the fly-wheel storage device.
Buffering of the electric energy from the DC voltage intermediate
circuit can be achieved with good efficiency. Aging as it occurs
with condensers is no concern for the fly-wheel energy storage
devices. They achieve furthermore, a high energy density and a
reaction speed in the range of milliseconds, and the number of
charging and discharging cycles is unlimited. The fly-wheel storage
device can further be modularized. Capacity increases can easily be
achieved by parallel arrangements of fly-wheel storage devices. In
any case, they have a long service life. The storage device also
can be overcharged for short periods of, for example, 60 seconds.
Its normal power storage capacity can be exceeded by up to 160%
which may be utilized, for example, during an emergency shut down.
If the fly-wheel storage device is overcharged, its energy may be
fed back to the power grid if the converter provided for the supply
of power to the DC voltage intermediate circuit 34 is a
correspondingly controllable converter.
[0059] As described, the fly-wheel storage device 48 can be
controlled via the determination of the energy balance of the
individual drives. But, it is also possible to operate the
fly-wheel storage device on the basis of the voltage measured in
the DC voltage intermediate circuit 34. When this voltage increases
energy is fed back from the DC voltage intermediate circuit 34 to
the fly-wheel storage device 48 that is the fly-wheel storage
device acts as a load. If the voltage in the DC voltage
intermediate circuit drops, the control unit provides for energy
transfer from the fly-wheel storage device 48 to the DC voltage
intermediate circuit 34. Load peaks within a press installation 1
are therefore uncoupled from the power grid 46.
[0060] In a preferred embodiment, the control unit controls the
converter arrangement, which is also called the "supply unit" and
determines whether energy should be supplied to the DC voltage
intermediate circuit, also called the DC bus, or energy should be
fed back therefrom to the fly-wheel storage device. Predetermined
power limits are taken into consideration in the process. The power
limits can be determined dynamically. The control unit can,
furthermore, monitor the rotational speed of the fly-wheel of the
fly-wheel storage device and the voltage in the DC voltage
intermediate circuit. The uptake of energy from the grid into the
DC lines and the back feeding of energy into the grid can be
controlled based on the following values:
[0061] upper limit of the fly-wheel speed of the storage
device;
[0062] lower limit of the fly-wheel speed of the storage
device;
[0063] desired value of the fly-wheel speed of the storage
device;
[0064] actual value of the fly-wheel speed of the storage
device;
[0065] desired value of the voltage of the DC intermediate circuit;
and,
[0066] actual value of the voltage of the DC intermediate
circuit.
[0067] The control occurs preferably with a view to minimizing the
grid load peaks that is providing for a uniform grid loading. For
activating the fly-wheel storage device, the drop and increase of
the intermediate circuit voltage can be monitored and utilized as
the voltage is the result of the difference between energy
consumption and energy delivery from the power grid. If limits are
set for the uptake of energy from the grid and feeding back of
energy into the grid, there remain load peak or feed back peak
differentials which are accommodated by the fly-wheel storage
device.
[0068] When the intermediate circuit voltage drops, the braking
procedure for the fly-wheels is initiated. The fly-wheel slowed
down until the intermediate circuit voltage has reached the
original value. When the intermediate circuit voltage rises, the
acceleration procedure for the fly-wheel is initiated. The
fly-wheel is accelerated until the intermediate circuit voltage has
reached the original design value.
[0069] The power limits for feeding energy into the power grid are
preferably set in such a way that long term speed of the fly-wheel,
averaged over several press strokes remains constant.
[0070] With the dynamic adjustability of the power limits for the
feeding energy back into the grid or taking it out of the grid, the
amount of the uptake and the feedback can be influenced. The limits
for the feedback and the uptake are different parameters and
dynamically controllable from without. By changing the power limits
of the supply unit, the point at which the energy supply support by
the fly-wheel energy storage device is activated can be varied. By
changing the feedback power limits of the supply unit, the point at
which energy is fed back into the fly-wheel storage device can be
varied.
[0071] With regard to the fly-wheel speed, the following operation
is possible: When the servo-press is switched on, first the
fly-wheel of the fly-wheel storage device is accelerated to the
design-speed which is, for example, about % of the maximum speed.
Upon reaching the desired speed, the fly-wheel storage device is
ready to supply energy with dropping speed or to take up energy by
acceleration of the fly-wheel from the desired speed to maximum
speed. In order to achieve an as uniform grid load as possible, the
power limits are reduced to such a degree that the load peaks are
accommodated as much as possible by the fly-wheel storage device up
to maximum fly-wheel speed. The fly-wheel speed varies between the
maximum speed and a minimum speed close to zero.
[0072] The energy profile, that is energy requirements over time,
of a servo-press depends on:
[0073] the deformation energy;
[0074] the movement profile; and,
[0075] the number of cycles per minute.
[0076] Therefore, an optimal determination of the power limits for
the manufacture of one part is not necessarily optimal for the
manufacture of another part. Therefore, the power limits of the
supply unit may be determined iteratively based on a base setting.
The power limits are reduced during initial operation to such an
extent and until the fly-wheel storage device reaches driving
operation the upper and the lower limit speeds. At the same time it
can be monitored whether the fly-wheel reaches again the desired
speed within a press cycle.
[0077] The data determined for a particular part or workpiece,
particularly, the power limits for feeding the DC lines from the
grid and for the feeding of energy from the DC lines back into the
grid can be recorded specifically for a particular workpiece in a
workpiece data storage device. Later this data can be retrieved, so
that it is not necessary to again determine the particular
operating values for that workpiece.
[0078] During a power grid failure, all servo-drives are shut down
in a controlled manner. The kinetic energy of the moving masses is
supplied by generator operation of the servo-motors to the DC
voltage intermediate circuit 34 and finally transferred to the
fly-wheel storage device 48. With a controlled slow-down or shut
down, consequently, the synchronization of all the servo-motors
and, as a result, particularly the synchronization between the part
transport and the plunger movement is maintained. The plungers can
be moved to a safe rest position in which they can, for example, be
locked. Data can be stored in an orderly way. Data processing units
can further be operated with the energy available from the
fly-wheel storage device. A destruction of, or damage to, the
converter and drive electronics by an uncontrolled increases in the
intermediate circuit voltage is effectively avoided. Also, a
de-synchronization of individual drives with chances of collision
of parts of the press installation is avoided.
* * * * *